This invention relates to an apparatus and process for die casting metal that includes driving a plunger core member into metal during solidification to densify the metal and concurrently to form a bore in a product casting. More particularly, the plunger core is adapted to be driven through the metal to substantially form a bore through the product casting that is surrounded by pore-free metal.
In U.S. patent application Ser. No. 391,106, an apparatus and process are described for die casting a metal article intended to have a bore therethrough surrounded by dense, pore-free metal. The apparatus comprises a plunger core adapted to be driven into a die cavity during metal solidification. The plunger core is driven towad a stationary core. The opposed tips of the plunger core and stationary core are preferably semispherical and displace or deflect metal laterally as the plunger core advances to collapse shrink pores in the metal that form during cooling and solidification. In addition to densifying the metal, the plunger core and the stationary core form recesses in the product casting that form the basis of a bore through the article. Although the apparatus and method are generally satisfactory for densification, a significant amount of metal remains between the recesses, so that a relatively expensive drilling operation is required to complete the bore. It is desired to reduce the cost of bore completion by eliminating the necessity for drilling while assuring densified metal about the bore along its entire length.
Therefore, it is an object of this invention to provide an improved process and apparatus for casting metal to form a cast article having a bore substantially therethrough and surrounded by densified metal substantially free of shrink porosity, which casting comprises driving a movable core member into the metal during solidification to substantially form the bore in the casting and concurrently to densify the metal about the bore along its entire length
More particularly, it is an object of this invention to provide a plunger core incorporated within a cavity-defining die casting apparatus and adapted to be driven into partially solidified metal within the cavity to form a bore in a product casting, which plunger core comprises a tip adapted to laterally displace metal as the core is driven into the metal, thereby densifying the metal about the bore. The tip is adapted to be received into a recess within an opposite cavity-defining wall such that the plunger core extends substantially through the cavity to substantially form the entire bore and further such that, at most, a thin metal flash remains between the tip and the wall, suitable for removal by a punching or similar operation to complete the bore without the necessity of a relatively expensive drilling operation. Metal is densified about the bore along substantially the entire length as a result of the plunger core being driven through the cavity.